Computational Design of Cyclic Peptide Inhibitors of a Bacterial Membrane Lipoprotein Peptidase.

There remains a critical need for new antibiotics against multi-drug-resistant Gram-negative bacteria, a major global threat that continues to impact mortality rates. Lipoprotein signal peptidase II is an essential enzyme in the lipoprotein biosynthetic pathway of Gram-negative bacteria, making it an attractive target for antibacterial drug discovery. Although natural inhibitors of LspA have been identified, such as the cyclic depsipeptide globomycin, poor stability and production difficulties limit their use in a clinical setting. We harness computational design to generate stable de novo cyclic peptide analogues of globomycin. Only 12 peptides needed to be synthesized and tested to yield potent inhibitors, avoiding costly preparation of large libraries and screening campaigns. The most potent analogues showed comparable or better antimicrobial activity than globomycin in microdilution assays against ESKAPE-E pathogens. This work highlights computational design as a general strategy to combat antibiotic resistance.

Blocking pathogenic Leptospira invasion with aptamer molecules targeting outer membrane LipL32 protein.

This study aimed to develop aptamers targeting LipL32, a most abundant lipoprotein in pathogenic Leptospira, to hinder bacterial invasion. The objectives were to identify high-affinity aptamers through SELEX and evaluate their specificity and inhibitory effects. SELEX was employed to generate LipL32 aptamers (L32APs) over 15 rounds of selection. L32APs' binding affinity and specificity for pathogenic Leptospira were assessed. Their ability to inhibit LipL32-ECM interaction and Leptospira invasion was investigated. Animal studies were conducted to evaluate the impact of L32AP treatment on survival rates, Leptospira colonization, and kidney damage. Three L32APs with strong binding affinity were identified. They selectively detected pathogenic Leptospira, sparing non-pathogenic strains. L32APs inhibited LipL32-ECM interaction and Leptospira invasion. In animal studies, L32AP administration significantly improved survival rates, reduced Leptospira colonies, and mitigated kidney damage compared to infection alone. This pioneering research developed functional aptamers targeting pathogenic Leptospira. The identified L32APs exhibited high affinity, pathogen selectivity, and inhibition of invasion and ECM interaction. L32AP treatment showed promising results, enhancing survival rates and reducing Leptospira colonization and kidney damage. These findings demonstrate the potential of aptamers to impede pathogenic Leptospira invasion and aid in recovery from Leptospira-induced kidney injury (190 words).

Pyridylpiperazine-based allosteric inhibitors of RND-type multidrug efflux pumps.

Efflux transporters of the RND family confer resistance to multiple antibiotics in Gram-negative bacteria. Here, we identify and chemically optimize pyridylpiperazine-based compounds that potentiate antibiotic activity in E. coli through inhibition of its primary RND transporter, AcrAB-TolC. Characterisation of resistant E. coli mutants and structural biology analyses indicate that the compounds bind to a unique site on the transmembrane domain of the AcrB L protomer, lined by key catalytic residues involved in proton relay. Molecular dynamics simulations suggest that the inhibitors access this binding pocket from the cytoplasm via a channel exclusively present in the AcrB L protomer. Thus, our work unveils a class of allosteric efflux-pump inhibitors that likely act by preventing the functional catalytic cycle of the RND pump.

Lipoproteins and cancer: The role of HDL-C, LDL-C, and cholesterol-lowering drugs.

Cholesterol is an amphipathic sterol molecule that is vital for maintaining normal physiological homeostasis. It is a relatively complicated molecule with 27 carbons whose synthesis starts with 2-carbon units. This in itself signifies the importance of this molecule. Cholesterol serves as a precursor for vitamin D, bile acids, and hormones, including estrogens, androgens, progestogens, and corticosteroids. Although essential, high cholesterol levels are associated with cardiovascular and kidney diseases and cancer initiation, progression, and metastasis. Although there are some contrary reports, current literature suggests a positive association between serum cholesterol levels and the risk and extent of cancer development. In this review, we first present a brief overview of cholesterol biosynthesis and its transport, then elucidate the role of cholesterol in the progression of some cancers. Suggested mechanisms for cholesterol-mediated cancer progression are plentiful and include the activation of oncogenic signaling pathways and the induction of oxidative stress, among others. The specific roles of the lipoprotein molecules, high-density lipoprotein (HDL) and low-density lipoprotein (LDL), in this pathogenesis, are also reviewed. Finally, we hone on the potential role of some cholesterol-lowering medications in cancer.

Quantitative Proteomics and Differential Protein Abundance Analysis after the Depletion of PEX3 from Human Cells Identifies Additional Aspects of Protein Targeting to the ER.

Protein import into the endoplasmic reticulum (ER) is the first step in the biogenesis of around 10,000 different soluble and membrane proteins in humans. It involves the co- or post-translational targeting of precursor polypeptides to the ER, and their subsequent membrane insertion or translocation. So far, three pathways for the ER targeting of precursor polypeptides and four pathways for the ER targeting of mRNAs have been described. Typically, these pathways deliver their substrates to the Sec61 polypeptide-conducting channel in the ER membrane. Next, the precursor polypeptides are inserted into the ER membrane or translocated into the ER lumen, which may involve auxiliary translocation components, such as the TRAP and Sec62/Sec63 complexes, or auxiliary membrane protein insertases, such as EMC and the TMCO1 complex. Recently, the PEX19/PEX3-dependent pathway, which has a well-known function in targeting and inserting various peroxisomal membrane proteins into pre-existent peroxisomal membranes, was also found to act in the targeting and, putatively, insertion of monotopic hairpin proteins into the ER. These either remain in the ER as resident ER membrane proteins, or are pinched off from the ER as components of new lipid droplets. Therefore, the question arose as to whether this pathway may play a more general role in ER protein targeting, i.e., whether it represents a fourth pathway for the ER targeting of precursor polypeptides. Thus, we addressed the client spectrum of the PEX19/PEX3-dependent pathway in both PEX3-depleted HeLa cells and PEX3-deficient Zellweger patient fibroblasts by an established approach which involved the label-free quantitative mass spectrometry of the total proteome of depleted or deficient cells, as well as differential protein abundance analysis. The negatively affected proteins included twelve peroxisomal proteins and two hairpin proteins of the ER, thus confirming two previously identified classes of putative PEX19/PEX3 clients in human cells. Interestingly, fourteen collagen-related proteins with signal peptides or N-terminal transmembrane helices belonging to the secretory pathway were also negatively affected by PEX3 deficiency, which may suggest compromised collagen biogenesis as a hitherto-unknown contributor to organ failures in the respective Zellweger patients.

Structure of the Human Cholesterol Transporter ABCG1.

ABCG1 is an ATP binding cassette (ABC) transporter that removes excess cholesterol from peripheral tissues. Despite its role in preventing lipid accumulation and the development of cardiovascular and metabolic disease, the mechanism underpinning ABCG1-mediated cholesterol transport is unknown. Here we report a cryo-EM structure of human ABCG1 at 4 Å resolution in an inward-open state, featuring sterol-like density in the binding cavity. Structural comparison with the multidrug transporter ABCG2 and the sterol transporter ABCG5/G8 reveals the basis of mechanistic differences and distinct substrate specificity. Benzamil and taurocholate inhibited the ATPase activity of liposome-reconstituted ABCG1, whereas the ABCG2 inhibitor Ko143 did not. Based on the structural insights into ABCG1, we propose a mechanism for ABCG1-mediated cholesterol transport.

Systematic review and meta-analysis of randomized controlled trials on the effects of obeticholic acid on the blood lipid profile: Insights into liver disorders and liver cancer.

AIM: Treatment with obeticholic acid (OCA) affects the blood lipid profile. Therefore, a meta-analysis of randomized controlled trials (RCTs) was performed to investigate the effects of OCA on blood lipids and lipoproteins. METHODS AND RESULTS: The electronic databases of PubMed, Web of Science, SCOPUS, and Google Scholar were searched. The mean differences were meta-analyzed to obtain a pooled weighted mean difference (WMD) and the 95% CI across the trials using the Der Simonian and Laird random-effects method. Six (6) articles with 10 trials for low-density lipoprotein cholesterol (LDL-C), and 8 trials for high-density lipoprotein cholesterol (HDL-C), total cholesterol (TC), and triglycerides (TG) levels were included in the meta-analysis. . Most studies were conducted in patients with liver dysregulation (fatty liver, liver cancer). The pooled results showed that the levels of TC (WMD: 6.357 mg/dl) and LDL-C (WMD: 6.067 mg/dl) increased while TG (WMD: -22.417 mg/dl) decreased after treatment with OCA. A slight but significant decrease was also observed for HDL-C levels (WMD: -1.492 mg/dl). A significant non-linear response was observed only between the TG levels and the length of intervention. Larger reductions in TG levels were observed over intervention durations of less than 3 weeks, but regarding interventions for more than 3 weeks, the impact on TG was modest. CONCLUSION: OCA administration causes significant increases in blood levels of TC and LDL-C while decreasing HDL-C and TG in humans. More study needed on liver cancer.

XFEL and NMR Structures of Francisella Lipoprotein Reveal Conformational Space of Drug Target against Tularemia.

Francisella tularensis is the causative agent for the potentially fatal disease tularemia. The lipoprotein Flpp3 has been identified as a virulence determinant of tularemia with no sequence homology outside the Francisella genus. We report a room temperature structure of Flpp3 determined by serial femtosecond crystallography that exists in a significantly different conformation than previously described by the NMR-determined structure. Furthermore, we investigated the conformational space and energy barriers between these two structures by molecular dynamics umbrella sampling and identified three low-energy intermediate states, transitions between which readily occur at room temperature. We have also begun to investigate organic compounds in silico that may act as inhibitors to Flpp3. This work paves the road to developing targeted therapeutics against tularemia and aides in our understanding of the disease mechanisms of tularemia.

Discovery of multidrug efflux pump inhibitors with a novel chemical scaffold.

Multidrug efflux is a major contributor to antibiotic resistance in Gram-negative bacterial pathogens. Inhibition of multidrug efflux pumps is a promising approach for reviving the efficacy of existing antibiotics. Previously, inhibitors targeting both the efflux transporter AcrB and the membrane fusion protein AcrA in the Escherichia coli AcrAB-TolC efflux pump were identified. Here we use existing physicochemical property guidelines to generate a filtered library of compounds for computational docking. We then experimentally test the top candidate coumpounds using in vitro binding assays and in vivo potentiation assays in bacterial strains with controllable permeability barriers. We thus identify a new class of inhibitors of E. coli AcrAB-TolC. Six molecules with a shared scaffold were found to potentiate the antimicrobial activity of erythromycin and novobiocin in hyperporinated E. coli cells. Importantly, these six molecules were also active in wild-type strains of both Acinetobacter baumannii and Klebsiella pneumoniae, potentiating the activity of erythromycin and novobiocin up to 8-fold.

Long-chain fatty acyl-coenzyme A suppresses hepatitis C virus infection by targeting virion-bound lipoproteins.

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis and end-stage liver diseases. Mature HCV virions are bound by host-derived lipoproteins. Lack of an HCV vaccine warrants a major role of antiviral treatment in the global elimination of hepatitis C. Although direct-acting antivirals (DAAs) are replacing the interferon-based treatment and have dramatically improved the cure rate, the presence of viral variants resistant to DAAs, HCV genotype/subtype-specific efficacy, and high cost of DAAs argue novel and affordable regimens. In this study, we identified the antiviral effects of long-chain fatty acyl-coenzyme A (LCFA-CoA) against the infections of HCV genotypes 1-6 through targeting mature HCV-bound lipoproteins, suggesting novel mechanism(s) of antiviral different from those used by host-targeting agents or DAAs. We found that the antiviral activity of LCFA-CoA relied on the long-chain saturated fatty acid and the CoA group, and was enhanced when combined with pegylated-interferon or DAAs. Importantly, we demonstrated that LCFA-CoA efficiently inhibited the infection of HCV variants carrying DAA-resistant mutations. The mechanistic study revealed that LCFA-CoA specifically abolished the attachment and binding steps and also inhibited the cell-to-cell viral transmission. LCFA-CoA targeted mature HCV-bound lipoproteins, but not apolipoproteins B or E. In addition, LCFA-CoA could also inhibit the infection of the dengue virus. Our findings suggest that LCFA-CoA could potentially serve as a supplement HCV therapy, particularly for the DAA-resistant HCV variants. Taken together, LCFA-CoA may be further developed to be a novel class of antivirals with mechanism(s), different from host-targeting agents or DAAs, of targeting the components associated with mature HCV virions.

Anti-tissue factor pathway inhibitor (TFPI) therapy: a novel approach to the treatment of haemophilia.

Novel approaches to the treatment of haemophilia are needed due to the limitations of the current standard of care, factor replacement therapy. Aspirations include lessening the treatment burden and effectively preventing joint damage. Treating haemophilia by restoring thrombin generation may be an effective approach. A promising target for restoring thrombin generation is tissue factor pathway inhibitor (TFPI), a multivalent Kunitz-type serine protease inhibitor that regulates tissue factor-induced coagulation via factor Xa-dependent feedback inhibition of the tissue factor-factor VIIa complex. Inhibition of TFPI reverts the coagulation process to a more primitive state evolutionarily, whilst regulation by other natural inhibitors is preserved. An aptamer and three monoclonal antibodies directed against TFPI have been investigated in clinical trials. As well as improving thrombin generation in the range associated with mild haemophilia, anti-TFPI therapies have the advantage of subcutaneous administration. However, the therapeutic window needs to be defined along with the potential for complications due to the novel mechanism of action. This review provides an overview of TFPI, its role in normal coagulation, the rationale for TFPI inhibition, and a summary of anti-TFPI therapies, previously or currently in development.

Neutralizing Antibody Assay Development with High Drug and Target Tolerance to Support Clinical Development of an Anti-TFPI Therapeutic Monoclonal Antibody.

Immunogenicity is a major challenge for protein therapeutics which can potentially reduce drug efficacy and safety and is often being monitored by anti-drug antibody (ADA) and neutralizing antibody (NAb) assays. Circulating targets and residual drugs in matrices can have significant impacts on accuracy of results from ADA and NAb assays, and sufficient drug and target tolerance for these assays are necessary. Here, we report the development of a competitive ligand binding (CLB) NAb assay for an anti-TFPI (tissue factor pathway inhibitor) monoclonal antibody (PF-06741086) with high drug and target tolerance to support ongoing clinical studies. A double acid affinity capture elution approach was used to mitigate drug interference, and a robust target removal strategy was employed to enhance target tolerance. The validated NAb assay has sensitivity of 313 ng/mL, drug tolerance of 50 µg/mL, and target tolerance of 1200 ng/mL. A step-by-step tutorial of assay development is described in this manuscript along with the rationale for using a high drug/target tolerant NAb assay. The NAb assay cut point factor obtained was 0.78. Other assay performance characteristics, e.g., precision and selectivity, are also discussed. This validated method demonstrated a superior drug and target tolerance to warrant specific and precise characterization of the NAb responses in support of ongoing clinical studies.

Antibodies in the Treatment of Haemophilia A-A Biochemical Perspective.

Replacement therapy has been proven effective in the management of bleedings in haemophilia A. Nevertheless, this approach comes with several shortcomings, like the need for frequent intravenous infusions and the development of neutralizing antibodies in 20 to 30% of the patients with severe haemophilia A replacement. This has led to the development of novel strategies to expand the spectrum of treatment options, some of which are based on antibody technology. These include a bispecific antibody that bridges enzyme factor IXa and substrate factor X, monoclonal antibodies that block the function of tissue factor pathway inhibitor, and a factor VIII-nanobody fusion protein with strongly enhanced von Willebrand factor binding. In this review, functional and mechanistic considerations on the use of these antibody variants will be discussed.

Identification of Binding Sites for Efflux Pump Inhibitors of the AcrAB-TolC Component AcrA.

The overexpression of multidrug efflux pumps is an important mechanism of clinical resistance in Gram-negative bacteria. Recently, four small molecules were discovered that inhibit efflux in Escherichia coli and interact with the AcrAB-TolC efflux pump component AcrA. However, the binding site(s) for these molecules was not determined. Here, we combine ensemble docking and molecular dynamics simulations with tryptophan fluorescence spectroscopy, site-directed mutagenesis, and antibiotic susceptibility assays to probe binding sites and effects of binding of these molecules. We conclude that clorobiocin and SLU-258 likely bind at a site located between the lipoyl and ß-barrel domains of AcrA.

Inhibiting Pneumococcal Surface Antigen A (PsaA) with Small Molecules Discovered through Virtual Screening: Steps toward Validating a Potential Target for Streptococcus pneumoniae.

The pneumococcal surface antigen A (PsaA) metal transporter protein provides manganese to bacterial cells. The X-ray crystal structures of PsaA, in both closed (Mn bound) and open (metal free) conformations, were explored with virtual screening to identify potential inhibitors of manganese transport. We pursued three strategies for inhibition: i) targeting a cavity close to the bound Mn to keep the metal in place; ii) targeting the metal-free Mn site to prevent metal uptake; and iii) targeting a potentially druggable allosteric site involving loops that translate between the conformations. Tiered assays were used to test the resulting 170 acquired hits: i) assay 1 tested the compounds' growth inhibition of the TIGR4 S. pneumoniae strain (ΔPsaA mutant control), yielding 80 compounds (MIC≤250 µm); ii) assay 2 tested if the addition of 20 µm Mn to inhibited cell cultures restored growth, yielding 21 compounds; and iii) assay 3 confirmed that the restored bacterial growth was Mn concentration dependent, as was the restoration of ΔPsaA growth, yielding 12 compounds with MICs of 125 µm or greater. It may be possible for a small molecule to inhibit PsaA, but we have not yet identified a compound with exemplary properties.

A first-in-human study of the safety, tolerability, pharmacokinetics and pharmacodynamics of PF-06741086, an anti-tissue factor pathway inhibitor mAb, in healthy volunteers.

Essentials Tissue factor pathway inhibitor (TFPI) is an antagonist of FXa and the TF-FVIIa complex. PF-06741086 is an IgG1 monoclonal antibody that targets the Kunitz-2 domain of TFPI. Single doses of PF-06741086 were evaluated in a phase 1 study in healthy volunteers. Data from this study support further investigation of PF-06741086 in individuals with hemophilia. SUMMARY: Background Tissue factor pathway inhibitor (TFPI) is a protease inhibitor of the tissue factor-activated factor VII complex and activated FX. PF-06741086 is a mAb that targets TFPI to increase clotting activity. Objectives This study was a randomized, double-blind, sponsor-open, placebo-controlled, single intravenous or subcutaneous dose escalation study to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of PF-06741086. Patients/Methods Volunteers who provided written informed consent were assigned to cohorts with escalating dose levels. Safety endpoints included treatment-emergent adverse events (TEAEs), infusion/injection site reactions, vital signs, electrocardiogram, and coagulation and hematology laboratory parameters. Pharmacokinetic (PK) and pharmacodynamic (PD) endpoints included exposures of PF-06741086 in plasma and measures of PF-06741086 pharmacology, respectively. Results Forty-one male volunteers were recruited overall. Thirty-two were dosed with PF-06741086 from 30 mg subcutaneously to 440 mg intravenously. All doses were safe and well tolerated. TEAEs were mild or moderate in severity, laboratory abnormalities were transient, there were no serious adverse events, there were no infusion/injection site reactions, and no dose escalation stopping criteria were met. Plasma exposures of PF-06741086 increased greater than proportionally with dose under the same dosing route. Coagulation pharmacology was demonstrated via total TFPI, dilute prothrombin time, D-dimer, prothrombin fragment 1 + 2 and thrombin generation assay parameters. Conclusions Single doses of PF-06741086 at multiple dose levels were safe and well tolerated in a healthy adult male population. The safety, PK and PD data from this study support progression to a multiple-dose study in hemophilic patients.

Inhibition of Tissue Factor Pathway Inhibitor (TFPI) as a Treatment for Haemophilia: Rationale with Focus on Concizumab.

Replacement therapy with missing factor (F) VIII or IX in haemophilia patients for bleed management and preventative treatment or prophylaxis is standard of care. Restoration of thrombin generation through novel mechanisms has become the focus of innovation to overcome limitations imposed by protein replacement therapy. Tissue factor pathway inhibitor (TFPI) is a multivalent Kunitz-type serine protease inhibitor that regulates tissue factor (TF)-induced coagulation through a FXa-dependent feedback inhibition of the TF.FVIIa complex in plasma and on endothelial surfaces. Concizumab is a monoclonal, humanised antibody, specific for the second Kunitz domain of TFPI that binds and inhibits FXa, abolishing the inhibitory effect of TFPI. Concizumab restored thrombin generation in FVIII and FIX deficient plasmas and decreased blood loss in a rabbit haemophilia model. Phase 1 single and multiple dose escalation studies in haemophilia patients demonstrated a dose dependent decrease in TFPI levels and a pro-coagulant effect with increasing d-dimers and prothrombin fragment 1 + 2. A dose dependent increase in peak thrombin and endogenous thrombin potential was observed with values in the normal range when plasma TFPI levels were nearly undetectable. A few haemophilia patients in the highest dose cohorts with complete inhibition of plasma TFPI showed a decreased fibrinogen concentration with normal levels of anti-thrombin and platelets and no evidence of thrombosis. Pharmacokinetic parameters were influenced by binding to the target (TFPI), demonstrating target mediated drug disposition. A trend towards decreasing bleeding tendency was observed and this preventative effect is being studied in Phase 2 studies with additional data gathered to improve our understanding of the therapeutic window and potential for thrombosis.

In vitro activity of the novel triazaacenaphthylene gepotidacin (GSK2140944) against MDR Neisseria gonorrhoeae.

Objectives: Increased antimicrobial resistance surveillance and new effective antimicrobials are crucial to maintain treatable gonorrhoea. We examined the in vitro activity of gepotidacin, a novel triazaacenaphthylene, and the effect of efflux pump inactivation on clinical Neisseria gonorrhoeae isolates and international reference strains (n = 252) and compared gepotidacin with antimicrobials currently or previously recommended for gonorrhoea treatment. Methods: MICs (mg/L) were determined by agar dilution (gepotidacin) or by Etest (seven other antimicrobials). The gyrA and parC genes were sequenced and the impact of inactivation of the MtrCDE, MacAB and NorM efflux pumps on gepotidacin MICs was examined. Results: Gepotidacin showed potent in vitro activity against all gonococcal isolates (n = 252; MIC ≤4 mg/L). The modal MIC, MIC50, MIC90 and MIC range of gepotidacin were 0.5, 0.5, 1 and 0.032-4 mg/L, respectively. Inactivation of the MtrCDE efflux pump, but not MacAB or NorM, decreased the gepotidacin MICs for most strains. No significant cross-resistance between gepotidacin and any other antimicrobials, including the fluoroquinolone ciprofloxacin, was identified. However, the ParC D86N mutation (possibly together with additional antimicrobial resistance mutation), which is associated with fluoroquinolone resistance, was associated with increased gepotidacin MICs. Conclusions: Gepotidacin demonstrated high in vitro activity against gonococcal strains, indicating that gepotidacin could potentially be an effective option for gonorrhoea treatment, particularly in a dual antimicrobial therapy regimen and for patients with resistance or allergy to extended-spectrum cephalosporins. Nevertheless, elucidating in vitro and in vivo resistance emergence and mechanisms in detail, together with further gonorrhoea clinical studies, ideally also including chlamydia and Mycoplasma genitalium are essential.

Translational Pharmacokinetic/Pharmacodynamic Characterization and Target-Mediated Drug Disposition Modeling of an Anti-Tissue Factor Pathway Inhibitor Antibody, PF-06741086.

Tissue factor pathway inhibitor (TFPI) exhibits multiple isoforms, which are known to present in multiple locations such as plasma, endothelium, and platelets. TFPI is an endogenous negative modulator of the coagulation pathway, and therefore, neutralization of TFPI function can potentially increase coagulation activity. A human monoclonal antibody, PF-06741086, which interacts with all isoforms of TFPI is currently being tested in clinic for treating hemophilia patients with and without inhibitors. To support clinical development of PF-06741086, pharmacokinetics (PK) and pharmacodynamics of PF-06741086 were characterized in monkeys. In addition, a mechanistic model approach was used to estimate PK parameters in monkeys and simulate PK profiles in human. The results show that PF-06741086 exhibited target-mediated drug disposition and had specific effects on various hemostatic markers including diluted prothrombin time, thrombin generation, and thrombin-antithrombin complex in monkeys after administration. The model-predicted and observed human exposures were compared retrospectively, and the result indicates that the exposure prediction was reasonable within less than 2-fold deviation. This study demonstrated in vivo efficacy of PF-06741086 in monkeys and the utility of a rational mechanistic approach to describe PK for a monoclonal antibody with complex target binding.

Postprandial remnant lipoproteins as targets for the prevention of atherosclerosis.

PURPOSE OF REVIEW: Oxidized low-density lipoprotein (Ox-LDL) and chylomicron remnants were previously proposed as the most atherogenic lipoproteins for the causal lipoproteins of atherosclerosis. However, there are still controversies on these hypothesizes. Therefore, we have proposed a new hypothesis based on our recent findings of remnant lipoproteins (RLPs) in postprandial plasma. RECENT FINDINGS: Plasma RLP-C and RLP-TG increased significantly after fat load. More than 80% of the increased triglycerides after fat load consisted of the triglycerides in RLP, which contained greater amount of apoB100 than apoB48 particles as mostly very low density lipoproteins (VLDL) remnants. The majority of lipoprotein lipase (LPL) in plasma was found in RLP as RLP-LPL complex, which is released into circulation after hydrolysis. LPL activity and concentration in plasma did not increase after food intake associated with the insufficient hydrolysis of chylomicrons and VLDL and resulted in the significant increase of RLP-TG. Plasma LPL was inversely correlated with RLP particle size and number. SUMMARY: VLDL remnants have been shown as the major atherogenic lipoproteins in postprandial plasma associated with LPL activity as the targets for prevention of atherosclerosis. We also proposed a new definition of RLPs, 'LPL bound TG-rich lipoproteins' based on the findings of RLP-LPL complex.